Smoking device with heating profile based on puff volume

ABSTRACT

A method of operating an aerosol-generating device is provided for generating an aerosol from an aerosol-forming substrate during a usage session, the device including a power supply to supply power to a heating element to heat the substrate, and a controller, the method including: monitoring a user interaction parameter indicative of use of the device during the session; using the user interaction parameter for controlling temperature of the heating element during the session; monitoring a parameter indicative of aerosol generation during the session; analyzing the monitored parameter to identify a user puff, the user puff defined by a puff start and a puff end; analyzing the monitored parameter during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff; and using the puff volume as the user interaction parameter for controlling temperature of the heater element.

The present disclosure relates to a method of operating an aerosol-generating device, and an aerosol-generating device. In particular, the disclosure relates to an aerosol-generating device and a method in which temperature of a heating element is controlled with reference to user interaction.

Aerosol-generating devices configured to generate an aerosol from an aerosol-forming substrate, such as a tobacco-containing substrate, are known in the art. Typically, an inhalable aerosol is generated by the transfer of heat from a heat source to a physically separate aerosol-forming substrate or material, which may be located within, around or downstream of the heat source. An aerosol-forming substrate may be a liquid substrate contained in a reservoir. An aerosol-forming substrate may be a solid substrate. An aerosol-forming substrate may be a component part of a separate aerosol-generating article configured to engage with an aerosol-generating device to form an aerosol. During consumption, volatile compounds are released from the aerosol-forming substrate by heat transfer from the heat source and entrained in air drawn through the aerosol-generating article. As the released compounds cool, they condense to form an aerosol that is inhaled by the consumer.

Some aerosol-generating devices are configured to provide user experiences that have a finite duration. The duration of a usage session may be limited, for example, to approximate the experience of consuming a traditional cigarette. Some aerosol-generating devices are configured to be used with separate, consumable, aerosol-generating articles. Such aerosol-generating articles comprise an aerosol-forming substrate or substrates that are capable of releasing volatile compounds that can form an aerosol. Aerosol-forming substrates are commonly heated to form an aerosol. As the volatile compounds in an aerosol-forming substrate are depleted, the quality of the aerosol produced may deteriorate. Thus, some aerosol-generating devices are configured to limit the duration of the usage session to help prevent generation of a lower quality aerosol from a substantially depleted aerosol-forming substrate of an aerosol-generating article. A user would inhale aerosol from such a known aerosol-generating device by the application of one or more puffs to the device during the usage session. Some known aerosol-generating devices may limit the duration of the usage session based upon when a number of puffs applied to the device in the session reaches a predetermined limit.

It is known to provide power to a heat source to heat an aerosol-forming substrate in accordance with a thermal profile which varies over the duration of a usage session. In effect, such known thermal profiles define a temperature variation for the heat source as a function of the time elapsed in the usage session. As an aerosol-forming substrate becomes more depleted during a usage session, more energy is required to extract the remaining volatile compounds of the substrate which form the aerosol. Thus, it is known to use a thermal profile which increases a target operating temperature for the heat source over the second half of a usage session. Known thermal profiles used in the operation of a heat source are based on an idealised, hypothetical usage session. The idealised usage session may be characterised by a predetermined length for the usage session. The idealised usage session may additionally be based upon an assumed or idealised puffing behaviour of a user; for example, on an assumption that successive puffs of consistent predetermined length are applied at a predetermined rate over a finite period of time. However, when a real-life usage session departs from the assumptions inherent in the idealised usage session, the use of such known thermal profiles to control the temperature of the heat source can lead to inefficient extraction of aerosol from the substrate and be detrimental to the overall user experience. By way of example, if a user applied puffs at a faster rate than assumed in the known thermal profile, this could result in the usage session being terminated earlier than anticipated in the idealised usage session. Consequently, the temperature of the heat source may never reach the levels required in the second half of the usage session to efficiently extract aerosol from the substrate.

It is therefore desired to overcome the deficiencies and limitations outlined above.

According to a first aspect of the present invention, there is provided a method of operating an aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session. The aerosol-generating device comprises a power supply for supplying power to a heating element to heat the aerosol-forming substrate, and a controller. The method comprises steps of, monitoring a user interaction parameter indicative of use of the aerosol-generating device during the usage session, and using the user interaction parameter as a parameter for controlling temperature of the heating element during the usage session. Thus, the temperature of the heating element during the usage session can be controlled by reference to the manner of usage of the user during the usage session.

The user interaction parameter may be indicative of a user puff, or the number of puffs taken by a user during the usage session. The user interaction parameter may be indicative of volume of aerosol generated during the usage session.

A value of the user interaction parameter may associated with a target operating temperature of the heating element.

The user interaction parameter may increase over the duration of the usage session. A cumulative value of the user interaction parameter may, therefore, be recorded during the usage session. The cumulative value of the user interaction parameter recorded during the usage session may be associated with a target operating temperature of the heating element. The cumulative value of the user interaction parameter may have a predetermined maximum threshold value, and when the maximum threshold value is reached during the usage session, the usage session may be terminated.

By associating the user interaction parameter, or the cumulative value of the user interaction parameter, with a corresponding target operating temperature for the heater, it may be possible to adjust the target operating temperature of the heater to take account of specific usage characteristics of an individual user. This contrasts with known devices and thermal profiles discussed above, in which the temperature of the heater is varied as a function of the time elapsed in a usage session. The ability to adjust the target operating temperature of the heater according to the specific usage characteristics of an individual user may allow for more efficient extraction of aerosol from the aerosol-forming substrate. In this way, efficient aerosol extraction from the substrate may be achieved regardless of (or with less dependence on) the manner in which an individual user interacts with the aerosol-generating device. Therefore, a user may be able to extract substantially all available aerosol from the substrate without being limited to, for example, applying idealised puffs at a predetermined rate. These advantages may also provide the user with an enhanced user experience over the usage session.

As used herein, the term “aerosol-generating device” refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-forming substrate may be part of an aerosol-generating article, for example part of a smoking article. An aerosol-generating device may comprise one or more components used to supply energy from a power supply to an aerosol-forming substrate to generate an aerosol. For example, an aerosol-generating device may be a heated aerosol-generating device. An aerosol-generating device may be an electrically heated aerosol-generating device or a gas-heated aerosol-generating device. An aerosol-generating device may be a smoking device that interacts with an aerosol-forming substrate of an aerosol-generating article to generate an aerosol that is directly inhalable into a user's lungs through the user's mouth.

As used herein, the term “aerosol-forming substrate” refers to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may be solid or liquid or comprise both solid and liquid components. An aerosol-forming substrate may be adsorbed, coated, impregnated or otherwise loaded onto a carrier or support. An aerosol-forming substrate may conveniently be part of an aerosol-generating article or smoking article.

An aerosol-forming substrate may comprise nicotine. An aerosol-forming substrate may comprise tobacco, for example may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. In preferred embodiments an aerosol-forming substrate may comprise homogenised tobacco material, for example cast leaf tobacco. An aerosol-forming substrate may comprise at least one aerosol-former, such as propylene glycol or glycerine.

As used herein, the term “usage session” refers to a period in which a series of puffs are applied by a user to extract aerosol from an aerosol-forming substrate.

As used herein, the term “cumulative aerosol volume” refers to the cumulative volume of aerosol generated during a usage session, relative to the start of that usage session.

The usage session may comprise a plurality of usage session phases, each one of the plurality of usage session phases ending when a cumulative value of the user interaction parameter reaches a predetermined threshold for that one of the plurality of usage session phases. For example, the usage session may consist of between 4 and 20 usage session phases, preferably between 8 and 14 usage session phases, for example 10, 11, 12, 13, 14 or 15 usage session phases. Each of the usage session phases may end when the value of the user interaction parameter, or a cumulative value of the user interaction parameter, meets a predetermined threshold. Such a threshold may be termed an intermediate threshold as it is reached during the usage session. For example, a first usage session phase may end after a cumulative volume of aerosol generated from the start of the usage session reaches a first predetermined threshold; a second usage session phase, subsequent to the first usage session phase, may end after a cumulative volume of aerosol generated from the start of the usage session reaches a second predetermined threshold; and so on until the end of the usage session.

The usage session may comprise a plurality of usage session phases, each one of the plurality of usage session phases ending when a cumulative value of a second user interaction parameter, different to the user interaction parameter, reaches a predetermined threshold for that one of the plurality of usage session phases. Thus, the second user interaction parameter that controls progression through the plurality of usage session phases may be different from the user interaction parameter used to control temperature of the heating element. For example, a second user interaction parameter may be representative of number of user puffs taken during the usage session, and the user interaction parameter may be representative of aerosol volume generated during the usage session. In one example, each user puff may be considered to be a usage session phase.

Advantageously, each of the usage session phases may be associated with a target operating temperature for the heating element. Thus, during a first usage session phase the heating element may have a first target operating temperature and during a second usage session phase the heating element may have a second target operating temperature. The second target operating temperature may be a higher temperature than the first target operating temperature, or a lower temperature than the first operating temperature, or the same temperature as the first operating temperature.

Advantageously, the aerosol-generating device may store a predetermined thermal profile defining a heating element temperature with respect to a value of the monitored user interaction parameter, for example a cumulative value of the user interaction parameter during the usage session. Where progression of the user interaction parameter during the usage session is associated with a progression through a plurality of usage session phases, the thermal profile may, thus, define a heating element temperature for each of the plurality of usage session phases. The operating temperature of the heating element during the usage session may then be controlled in accordance with the predetermined thermal profile.

The predetermined thermal profile may be stored in a controller used to control the power supply. Alternatively, the predetermined thermal profile may be stored in a memory module accessible to such a controller.

Advantageously, the method may comprise associating a usage session phase with a corresponding target operating temperature for the heater based on the value of the user interaction parameter; and for the usage session phase, controlling the supply of power from the power supply in order to adjust the temperature of the heater to the target operating temperature associated with the usage session phase.

The temperature of the heating element may be controlled with reference to the user interaction parameter and a value of at least one further parameter monitored during the usage session. The at least one further parameter may be time. Thus, the temperature of the heating element may be controlled with reference to both the user interaction parameter and a value of time monitored during the usage session. In this way it may be possible to control the temperature of the heating element to take account of both change in the value of the user interaction parameter and rate of change of the value of the user interaction parameter. Depending on rate of change of the user interaction parameter, the controller may apply a positive or negative correction to a target operating temperature suggested by the predetermined thermal profile. For example, a usage session may be divided into six usage session phases determined by a cumulative value of volume of aerosol generated during the usage session.

Each of the usage session phases may be associated with a target operating temperature for the heating element in accordance with a predetermined thermal profile. The predetermined thermal profile may provide an optimised thermal profile for generation of aerosol over the duration of the usage session. The predetermined thermal profile may provide an optimised thermal profile for generation of aerosol over the duration of the usage session if the user interacts with the aerosol-generating device in accordance with a predetermined usage profile. The predetermined usage profile may provide an expected progression of the user interaction parameter over the duration of the usage session. A user may, however, interact with the aerosol-generating device in a manner that causes the real time values of the user interaction parameter to vary from those expected by the predetermined usage profile. In this circumstance, the controller may be programmed to make modifications to the predetermined thermal profile to take account of variations in actual values of the user interaction parameter at a point in the usage session compared with an expected value of the user interaction parameter at that point as predicted by the predetermined usage profile.

As an example, the predetermined thermal profile may be optimised for a predetermined rate of aerosol generation during the usage session. The predetermined rate of aerosol generation may be provided as a predetermined usage profile. If a user, however, takes intense or frequent puffs, aerosol may be generated at a rate higher than that assumed by the predetermined usage profile. In this circumstance a modification may be made to the target operating temperature, for example the target operating temperature associated with one of the usage phases, to account for a higher rate of aerosol generation. Such a correction may be triggered, for example, if the time taken between the start of one of the usage session phases and the start of the next one of the usage session phases is lower than a predetermined time. Conversely, if a user takes weaker or infrequent puffs, aerosol may be generated at a rate lower than the assumed consistent rate. In this circumstance, a modification may be made to the target operating temperature, for example the target operating temperature associated with one of the usage phases, to account for a lower rate of aerosol generation. Such a modification may be triggered, for example, if the time taken between the start of one of the usage session phases and the start of the next one of the usage session phases is greater than a predetermined time. Thus, temperature of the heating element may be controlled with respect to both a value of the user interaction parameter and time, for example a value of the user interaction parameter and a value indicative of rate of change of the user interaction parameter. Modification of a target operating temperature may be triggered by variances in time interval between successive puffs. Modification of a target operating temperature may be triggered by variances in the rate of generation of aerosol during the usage session. Depending on the manner of user interaction with the device over the duration of the usage session, target operating temperatures may be modified to be higher for some portions of the usage session and lower for other portions of the usage session.

Thus, the method may comprise steps of monitoring a user interaction parameter indicative of use of the aerosol-generating device during the usage session, a value of the user interaction parameter being associated with a target operating temperature of the heating element, monitoring a further parameter, for example time, and using the user interaction parameter and the further parameter, for example time, to control temperature of the heating element during the usage session. The controller may be programmed to use monitored values of the further parameter to determine whether a modification of the target operating temperature is implemented. The controller may be programmed to use a value indicative of rate of change of the user interaction parameter to determine whether a modification of the target operating temperature is implemented.

Advantageously, the user interaction parameter may be indicative of volume of aerosol released by the aerosol-forming substrate during the usage session. The method may, for example, comprise steps of monitoring a parameter indicative of aerosol generation during the usage session, analysing the monitored parameter indicative of aerosol generation to identify a user puff, the user puff defined by a puff start and a puff end, analysing the monitored parameter indicative of aerosol generation during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff, and using the puff volume as the user interaction parameter for controlling temperature of the heater element.

The method may comprise the steps of, analysing the monitored parameter indicative of aerosol generation to identify a plurality of user puffs performed during the usage session, each of the plurality of user puffs having a puff start and a puff end determined by analysing the monitored parameter indicative of aerosol generation. The method may further comprise steps of, analysing the monitored parameter indicative of aerosol generation during each of the plurality of identified user puffs to calculate a puff volume for each of the plurality of user puffs, determining a cumulative puff volume of aerosol generated during each of the plurality of identified user puffs, and using the cumulative puff volume as the user interaction parameter for controlling temperature of the heater element.

An aerosol-forming substrate, for example an aerosol-forming substrate of an aerosol-generating article, may have a maximum volume of aerosol intended for delivery during a usage session. As aerosol is depleted from the aerosol-forming substrate, an optimum aerosol-generating temperature may change. The rate at which aerosol is delivered during the usage session may be heavily influenced by the manner in which the user interacts with the device during the usage session. For example, a user who takes a high number of puffs in a short time may deplete available aerosol more quickly than a user who takes fewer puffs in the same time period, assuming that the intensity of puffs remains the same. Likewise, a user who takes ten long puffs, or high intensity puffs, may deplete available aerosol more quickly than a user who takes ten short puffs, or low intensity puffs. Controlling the operating temperature of the heating element during the usage session with reference to a user interaction parameter indicative of volume of aerosol generated may allow optimisation of the operating temperature over the duration of the usage session, irrespective of the manner in which the user interacts with the device.

A volume of aerosol generated in response to an applied puff may be determined directly or indirectly. The volume may be determined directly by use of an airflow sensor or the like. Preferably however, the volume is determined indirectly by use of a parameter indicative of aerosol generation during a usage session. The parameter indicative of aerosol generation may be representative of power supplied by the power supply. Current, voltage, or both current and voltage, supplied to a heater may be parameters representative of power. For example, a power supply may supply power to maintain a heater at a predetermined temperature during a usage session. If a user puffs on the device to generate an aerosol, the heater cools and a greater amount of power is required to maintain the heater at the predetermined temperature. Thus, by monitoring a parameter representative of power supplied by the power supply, a value indicative of real time aerosol generation may be recorded. A function of the monitored parameter indicative of aerosol generation may be calculated in real time and evaluated to determine puff volume.

The step of analysis of the monitored parameter may comprise steps of calculating a first characteristic of the monitored parameter and analysing the first characteristic to determine a puff start and a puff stop. The step of analysis of the monitored parameter may comprise steps of calculating a second characteristic of the monitored parameter and analysing both the first characteristic and the second characteristic to determine the puff start and the puff stop. The more accurately a puff start and a puff stop can be determined, the more accurate a calculation of puff volume can be.

A puff start may be determined to have occurred when the first characteristic and the second characteristic satisfy one or more predetermined conditions. A puff end may be determined to have occurred when the first characteristic and the second characteristic satisfy one or more predetermined conditions.

The first characteristic may be a first moving average value, first moving median value, or any other suitable signal characteristic value, of the monitored parameter computed on a first time window having a first time window duration. The second characteristic may be a second moving average value, second moving median value, or any other suitable signal characteristic value, of the monitored parameter computed on a second time window having a second time window duration, the second time window duration being different to the first time window duration.

A puff start may be determined when the first characteristic, for example the first moving average value, and the second characteristic, for example the second moving average value, meet a predetermined relationship with respect to each other. For example, the first time window duration may be shorter than the second time window duration and a puff start may be determined when the first moving average increases with respect to the second moving average and reaches a puff start value in which the first moving average equals the second moving average plus a first predetermined puff start constant.

A puff end may be determined when the first characteristic, for example the first moving average value, and the second characteristic, for example the second moving average value, meet a predetermined relationship with respect to each other. For example, a puff end may be determined when the first moving average decreases with respect to the second moving average, after the detection of a puff start, and reaches a puff end value in which the first moving average is greater than the second moving average minus a first predetermined puff end constant, and the second moving average is lesser than the value of the second moving average at puff start plus a second predetermined puff end constant.

The, or each, puff volume may be determined by integration of a curve representing the monitored parameter as a function of time between the, or each, puff start and the, or each, puff end. Puff volume, or cumulative puff volume, may be used as the user interaction parameter.

The first characteristic may be a first moving average value of the monitored parameter computed on a first time window having a first time window duration. The first time window duration is preferably a time of between 20 ms and 1000 ms, for example between 100 ms and 500 ms, or between 200 ms and 500 ms. The first window time duration may be about 250 ms, or about 300 ms, or about 350 ms, or about 400 ms, or about 450 ms.

The second characteristic may be a second moving average value of the monitored parameter computed on a second time window having a second time window duration, the second time window duration being different to the first time window duration. The second time window duration is preferably a time of between 100 ms and 2000 ms, for example between 500 ms and 1500 ms, or between 800 ms and 1400 ms. The second window time duration may be about 850 ms, or about 900 ms, or about 950 ms, or about 1000 ms, or about 1050 ms, or about 1100 ms, or about 1200 ms.

The first time window duration may be shorter that the second time window duration and a puff start may be determined when the first moving average increases with respect to the second moving average and reaches a puff start value in which the first moving average equals the second moving average plus a first predetermined puff start constant. The puff start constant may be, preferably, an empirically determined constant. The puff start constant may, alternatively, be a calculated constant.

A puff end may be determined when the first moving average decreases with respect to the second moving average, after the detection of a puff start, and reaches a puff end value in which the first moving average is greater than the second moving average minus a first predetermined puff end constant, and the second moving average is lesser than the value of the second moving average at puff start plus a second predetermined puff end constant. The first predetermined puff end constant and the second predetermined puff end constant may be, preferably, empirically determined constants. The first predetermined puff end constant and the second predetermined puff end constant may be, alternatively, calculated constants.

It may be possible that general noise in the monitored parameter means that criteria for a puff start are met when a genuine puff has not taken place. In order to minimise recording of such events as puffs, one or more predetermined validation conditions may be required to be met, after a puff start has been determined, to verify that a puff has taken place. A validation condition may be termed a trigger. Unless the validation condition, or each validation condition, is met, a puff is not recorded. As an example, once a puff start has been determined, a valid puff may only be recorded if a first validation condition is met and a puff end is detected. As a further example, once a puff start has been determined, a valid puff may only be recorded if a first validation condition is met, and a second validation is met, and a puff end is detected.

According to an aspect of the present invention there is provided, an aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session. The aerosol-generating device comprises a power supply for supplying power to generate the aerosol, and a controller configured to monitor a user interaction parameter indicative of use of the aerosol-generating device during the usage session, and use the user interaction parameter to control the temperature of the heating element during the usage session. The aerosol-generating device may be configured to perform any method described above.

The aerosol-generating device may be configured to monitor a parameter indicative of aerosol generation during operation of the aerosol-generating device and analyse the monitored parameter to identify a user puff. The user puff may be defined by a puff start and a puff end.

The aerosol-generating device may be configured to analyse the monitored parameter during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff. The aerosol-generating device may be configured to control the temperature of the heating element based on the calculated puff volume.

The aerosol-generating device may be configured to control the temperature of the heating element during a usage session with reference to a cumulative value of puff volume generated during the usage session. The aerosol-generating device may be configured to control the temperature of the heating element during a usage session with reference to rate of change of a cumulative value of puff volume generated during the usage session. The aerosol-generating device may be configured to control the temperature of the heating element during a usage session with reference to both a cumulative value of puff volume generated during the usage session and a rate of change of the cumulative value of puff volume generated during the usage session.

The aerosol-generating device may comprise a heater and the monitored parameter may be, or may be representative of, power supplied to the heater during operation of the aerosol-generating device. The heater may be an induction heater and the monitored parameter may be representative of energy absorbed by a susceptor. The heater may be a resistance heater and the monitored parameter may be representative of energy supplied to the resistance heater. The aerosol-generating device is preferably configured to receive an aerosol-generating article comprising the aerosol-forming substrate. The heating element may be comprised in the aerosol-generating article, for example, the heating element may be a susceptor forming part of the aerosol-generating article.

According to an aspect of the invention there is provided an aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session. The aerosol-generating device comprises a power supply for supplying power to generate the aerosol, and a controller. The aerosol-generating device comprises a computer readable medium containing instructions to carry out a method of monitoring a user interaction parameter indicative of use of the aerosol-generating device during the usage session, and using the user interaction parameter as a parameter for controlling temperature of the heating element during the usage session. The computer readable medium may comprise instructions to carry out any method described above.

The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

Example Ex1. A method of operating an aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising;

-   -   a power supply for supplying power to a heating element to heat         the aerosol-forming substrate, and     -   a controller;     -   the method comprising steps of,     -   monitoring a user interaction parameter indicative of use of the         aerosol-generating device during the usage session, and     -   using the user interaction parameter as a parameter for         controlling temperature of the heating element during the usage         session.

Example Ex2. A method according to example Ex1 in which a value of the user interaction parameter is associated with a target operating temperature of the heating element.

Example Ex3. A method according to example Ex1 or Ex2 in which a cumulative value of the user interaction parameter recorded during the usage session is associated with a target operating temperature of the heating element.

Example Ex3A. A method according to example Ex2 or Ex3 in which the controller is configured to monitor a rate of change of the user interaction parameter and to modify the target operating temperature for any value of the user interaction parameter, or any cumulative value of the user interaction parameter, based on the rate of change of the user interaction parameter.

Example Ex4. A method according to any preceding example in which a cumulative value of the user interaction parameter has a predetermined maximum threshold value, and when the maximum threshold value is reached during the usage session, the usage session is terminated.

Example Ex5. A method according to any preceding example in which the usage session comprises a plurality of usage session phases, each one of the plurality of usage session phases ending when a cumulative value of the user interaction parameter reaches a predetermined threshold for that one of the plurality of usage session phases.

Example Ex6. A method according to example Ex5 in which the usage session consists of between 4 and 20 usage session phases, preferably between 8 and 14 usage session phases, for example 10, 11, 12, 13, 14 or 15 usage session phases.

Example Ex7. A method according to example Ex5 or Ex6 in which each of the usage session phases is associated with a target operating temperature for the heating element.

Example Ex8. A method according to any preceding example, in which the aerosol-generating device stores a predetermined thermal profile defining a heating element temperature with respect to a value of the monitored user interaction parameter, for example a cumulative value of the user interaction parameter during the usage session.

Example Ex9. A method according to example Ex8 in which the operating temperature of the heating element during the usage session is controlled in accordance with the predetermined thermal profile.

Example Ex10. A method according to any preceding example in which the temperature of the heating element is controlled with reference to the user interaction parameter and a value of at least one further parameter monitored during the usage session.

Example Ex11. A method according to example Ex10 in which the temperature of the heating element is controlled with reference to the user interaction parameter and a value of time monitored during the usage session.

Example Ex11A. A method according to example Ex11 in which the temperature of the heating element is controlled, at least partially, with reference to a rate of change of the user interaction parameter.

Example Ex12. A method according to any preceding example in which the user interaction parameter is indicative of volume of aerosol released by the aerosol-forming substrate during the usage session.

Example Ex13. A method according to any preceding example comprising steps of, monitoring a parameter indicative of aerosol generation during the usage session,

-   -   analysing the monitored parameter indicative of aerosol         generation to identify a user puff, the user puff defined by a         puff start and a puff end,     -   analysing the monitored parameter indicative of aerosol         generation during the user puff to calculate a puff volume, the         puff volume being a volume of aerosol generated during the user         puff, and     -   using the puff volume as the user interaction parameter for         controlling temperature of the heater element.

Example Ex14. A method according to any preceding example comprising the steps of, analysing the monitored parameter indicative of aerosol generation to identify a plurality of user puffs performed during the usage session, each of the plurality of user puffs having a puff start and a puff end determined by analysing the monitored parameter indicative of aerosol generation.

Example Ex15. A method according to example Ex14 comprising steps of, analysing the monitored parameter indicative of aerosol generation during each of the plurality of identified user puffs to calculate a puff volume for each of the plurality of user puffs, determining a cumulative puff volume of aerosol generated during each of the plurality of identified user puffs, and using the cumulative puff volume as the user interaction parameter for controlling temperature of the heater element.

Example Ex16. A method according to any preceding example in which a function of the monitored parameter indicative of aerosol generation is calculated in real time and evaluated to determine puff volume.

Example Ex17. A method according to any preceding example in which the step of analysis of the monitored parameter indicative of aerosol generation comprises steps of calculating a first characteristic of the monitored parameter indicative of aerosol generation and analysing the first characteristic to determine a puff start and a puff stop.

Example Ex18. A method according to example Ex17 in which the step of analysis of the monitored parameter indicative of aerosol generation comprises steps of calculating a second characteristic of the monitored parameter indicative of aerosol generation and analysing both the first characteristic and the second characteristic to determine the puff start and the puff stop.

Example Ex19. A method according to example Ex18 in which a puff start is determined when the first characteristic and the second characteristic satisfy one or more predetermined conditions.

Example Ex20. A method according to example Ex19 or Ex20 in which a puff end is determined when the first characteristic and the second characteristic satisfy one or more predetermined conditions.

Example Ex21. A method according to any of examples Ex17 to Ex20 in which the first characteristic is a first moving average value of the monitored parameter computed on a first time window having a first time window duration.

Example Ex22. A method according to any of examples Ex18 to Ex21 in which the second characteristic is a second moving average value of the monitored parameter indicative of aerosol generation computed on a second time window having a second time window duration, the second time window duration being different to the first time window duration.

Example Ex23. A method according to example Ex22 in which a puff start is determined when the first moving average value and the second moving average value meet a predetermined relationship with respect to each other.

Example Ex24. A method according to example Ex23 in which the first time window duration is shorter that the second time window duration and a puff start is determined when the first moving average increases with respect to the second moving average and reaches a puff start value in which the first moving average equals the second moving average plus a first predetermined puff start constant.

Example Ex25. A method according to example Ex24 in which a puff end is determined when the first moving average decreases with respect to the second moving average, after the detection of a puff start, and reaches a puff end value in which the first moving average is greater than the second moving average minus a first predetermined puff end constant, and the second moving average is lesser than the value of the second moving average at puff start plus a second predetermined puff end constant.

Example Ex26. A method according to any of examples Ex17 to Ex20 in which the first characteristic is a first moving median value of the monitored parameter indicative of aerosol generation computed on a first time window having a first time window duration.

Example Ex27. A method according to any of examples Ex18 to Ex21 and Ex26 in which the second characteristic is a second moving median value of the monitored parameter indicative of aerosol generation computed on a second time window having a second time window duration, the second time window duration being different to the first time window duration.

Example Ex28. A method according to example Ex27 in which a puff start is determined when the first moving median value and the second moving median value meet a predetermined relationship with respect to each other.

Example Ex29. A method according to example Ex28 in which the first time window duration is shorter than the second time window duration and a puff start is determined when the first moving median increases with respect to the second moving median and reaches a puff start value in which the first moving median equals the second moving median plus a first predetermined puff start constant.

Example Ex30. A method according to example Ex29 in which a puff end is determined when the first moving median decreases with respect to the second moving median, after the detection of a puff start, and reaches a puff end value in which the first moving median is greater than the second moving median minus a first predetermined puff end constant, and the second moving median is lesser than the value of the second moving median at puff start plus a second predetermined puff end constant.

Example Ex31. A method according to any preceding example in which the monitored parameter indicative of aerosol generation is analysed to detect at least one validation condition, or trigger, occurring after the puff start and before the puff end, detection of the at least one validation condition, or trigger, being necessary for a valid puff to be recorded.

Example Ex32. A method according to example Ex31 in which a validation condition, or trigger, is determined when the first characteristic and the second characteristic satisfy one or more predetermined conditions.

Example Ex33. A method according to any preceding example in which the or each puff volume is determined by integration of a curve representing the monitored parameter indicative of aerosol generation as a function of time between the puff or each puff start and the or each puff end.

Example Ex34. An aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising; a power supply for supplying power to generate the aerosol, and a controller configured to monitor a user interaction parameter indicative of use of the aerosol-generating device during the usage session, and use the user interaction parameter to control the temperature of the heating element during the usage session.

Example Ex35. An aerosol-generating device according to example Ex34 configured to perform the method as defined in any of examples Ex1 to Ex33.

Example Ex36. An aerosol-generating device according to example Ex34 or Ex35, in which the device is configured to monitor a parameter indicative of aerosol generation during operation of the aerosol-generating device, analyse the monitored parameter to identify a user puff, the user puff defined by a puff start and a puff end, analyse the monitored parameter during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff, and control the temperature of the heating element based on the calculated puff volume.

Example Ex37. An aerosol-generating device according to any of examples Ex34 to Ex36 in which the device comprises a heater and the monitored parameter is, or is representative of, power supplied to the heater during operation of the aerosol-generating device.

Example Ex38. An aerosol-generating device according to example Ex37 in which the heater is an induction heater, the heating element is a susceptor, and the monitored parameter is representative of energy absorbed by the susceptor.

Example Ex39. An aerosol-generating device according to example Ex37 in which the heater is a resistance heater, the heating element is a resistive heating element, and the monitored parameter is representative of energy supplied to the resistance heater.

Example Ex40. An aerosol-generating device according to any of examples Ex34 to Ex39 configured to receive an aerosol-generating article comprising the aerosol-forming substrate.

Example Ex41. An aerosol-generating device according to example Ex40 in which the heating element is comprised in the aerosol-generating article, for example, in which the heating element is a susceptor comprised in the aerosol-generating article.

Example Ex42. An aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising; a power supply for supplying power to generate the aerosol, and a controller, the aerosol-generating device comprising a computer readable medium containing instructions to carry out a method of monitoring a user interaction parameter indicative of use of the aerosol-generating device during the usage session, and using the user interaction parameter as a parameter for controlling temperature of the heating element during the usage session.

Example Ex43. An aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising; a power supply for supplying power to generate the aerosol, and a controller, the aerosol-generating device comprising a computer readable medium containing instructions to carry out a method according to any of examples Ex1 to Ex33.

Examples will now be further described with reference to the figures, in which:

FIG. 1 illustrates a schematic side view of an aerosol-generating device;

FIG. 2 illustrates a schematic upper end view of the aerosol-generating device of FIG. 1 ;

FIG. 3 illustrates a schematic cross-sectional side view of the aerosol-generating device of FIG. 1 and an aerosol-generating article for use with the device;

FIG. 4 illustrates a method in accordance with the present disclosure, in which the target operating temperature for the heater is adjusted as a function of cumulative aerosol volume generated during a usage session;

FIG. 5 illustrates a thermal profile according to the present disclosure, in which the target operating temperature for the heater is defined as a function of cumulative aerosol volume generated during a usage session;

FIG. 6 is a flow diagram illustrating a method of controlling operating temperature of an aerosol-generating device by detecting puffs and calculating cumulative aerosol volume generated during a usage session;

FIG. 7 is a graph illustrating power as a function of time during a user puff, and two moving averages of the power curve, in particular illustrating the detection point of a puff;

FIG. 8 is a graph illustrating power as a function of time during a user puff, and two moving averages of the power curve, in particular illustrating a second trigger point;

FIG. 9 is a graph illustrating power as a function of time during a user puff, and two moving averages of the power curve, in particular illustrating the detection of the end point of a puff;

FIG. 10 is a graph illustrating the detection of a puff, including identification of various trigger points used to verify the puff; and

FIG. 11 is a graph illustrating the calculation of energy by integrating the power signal during the detected puff.

An exemplary aerosol-generating device 10 is a hand-held aerosol generating device, and has an elongate shape defined by a housing 20 that is substantially circularly cylindrical in form (see FIGS. 1, 2 and 3 ). The aerosol-generating device 10 comprises an open cavity 25 located at a proximal end 21 of the housing 20 for receiving an aerosol-generating article 30 comprising an aerosol-forming substrate 31. The aerosol-generating device 10 has a battery 26, control electronics 27 and a memory module 28 located within the housing 20. The memory module 28 is readable and writable in use. An electrically-operated heater 40 is arranged within the device 10 to heat at least an aerosol-forming substrate portion 31 of an aerosol-generating article 30 when the aerosol-generating article is received in the cavity 25. The memory module 28 stores a thermal profile accessible to the control electronics 27 during use of the device 10. The thermal profile defines how a target operating temperature for the heater 40 varies in a usage session.

The aerosol-generating device is configured to receive a consumable aerosol-generating article 30. The aerosol-generating article 30 is in the form of a cylindrical rod and comprises an aerosol-forming substrate 31 (see FIG. 3 ). The aerosol-forming substrate 31 is a solid aerosol-forming substrate comprising tobacco. The aerosol-generating article 30 further comprises a mouthpiece such as a filter 32 arranged in coaxial alignment with the aerosol-forming substrate 31 within the cylindrical rod. The aerosol-generating article 30 has a diameter substantially equal to the diameter of the cavity 25 of the device 10 and a length longer than a depth of the cavity 25, such that when the article 30 is received in the cavity 25 of the device 10, the mouthpiece 32 extends out of the cavity 25 and may be drawn on by a user, similarly to a conventional cigarette.

In use, a user inserts the article 30 into the cavity 25 of the aerosol-generating device 10 and turns on the device 10 by pressing a user button 50 (see FIG. 1 ) to activate the heater 40 to start a usage session. The heater 40 heats the aerosol-forming substrate 31 of the article 30 such that volatile compounds of the aerosol-forming substrate are released and atomised to form an aerosol. The user draws on the mouthpiece of the article 30 and inhales the aerosol generated from the heated aerosol-forming substrate 31. After activation, the temperature of the heater 40 increases from an ambient temperature to a predetermined temperature for heating the aerosol-forming substrate. The predetermined temperature is defined in the thermal profile stored in memory 28. After activation and over the course of the usage session, the control electronics 27 of the device 10 access the thermal profile stored in the memory module 28 so as to control the supply of power from the battery 26 to the heater 40 to adjust the heater temperature in accordance with the thermal profile. The heater 40 continues to heat the aerosol-generating article 30 until an end of the usage session, when the heater is deactivated and cools. In some specific examples the heater 40 may be a resistance heating element. In some specific examples the heater 40 may be a susceptor arranged within a fluctuating magnetic field such that it is heated by induction.

At the end of the usage session, the article 30 is removed from the device 10 for disposal, and the device 10 may be coupled to an external power source for charging of the battery 26 of the device 10.

The aerosol-generating article 30 for use with the device 10 has a finite quantity of aerosol-forming substrate 31 and, thus, a usage session needs to have a finite duration to prevent a user trying to produce aerosol when the aerosol-forming substrate has been depleted. A usage session is configured to have a maximum duration determined by a maximum time period from the start of the usage session. A usage session is also configured to have a duration of less than the maximum time period if a user interaction parameter recorded during the usage session reaches a threshold before elapse of the maximum time period. In a specific example the user interaction parameter is representative of a cumulative volume of aerosol generated over the duration of the usage session. A maximum aerosol generation threshold, for example a threshold of 660 ml, is defined for the cumulative volume of aerosol. So, for this specific example, the aerosol-generating device 10 is configured such that each usage session has a maximum duration defined by the first to occur of: i) 6 minutes from activation of the usage session, or ii) a total of 660 ml of aerosol being generated during the usage session.

FIG. 4 schematically illustrates a method 100 in accordance with the present disclosure. The method 100 is performed by the aerosol-generating device 10 of the present disclosure when a user applies a series of puffs to the aerosol-generating device 10 during a usage session. During each puff, a volume of aerosol is generated. The volume of aerosol generated is calculated and a cumulated volume of aerosol recorded over the duration of the usage session. Cumulative volume of aerosol is used as a user interaction parameter. In step 101, a first threshold cumulative volume of aerosol is associated with a corresponding target operating temperature for the heater 40. In step 102 the supply of power from the battery 26 is controlled by the control electronics 27 so as to adjust the temperature of the heater 40 to the target operating temperature associated with the first threshold volume of aerosol generated.

Steps 101, 102 of method 100 are repeated for second, third, and fourth threshold cumulative volumes of aerosol, and so on until termination of the usage session. The method 100 thereby enables the temperature of the heater 40 to be adjusted as a function of the cumulative volume of aerosol generated during a usage session.

The method 100 may be performed by a combination of the control electronics 27 and a thermal profile stored in the memory module 28. In the course of a usage session, the control electronics 27 would access the memory module 28 to read the thermal profile, and then control the supply of power from the power supply 26 in order to adjust the temperature of the heater 40 according to instructions provided in the thermal profile.

FIG. 5 illustrates an example of a thermal profile for use in performing a method as disclosed herein, for example in performing the method of FIG. 4 with aerosol-generating device 10. The thermal profile of FIG. 5 defines a target operating temperature for each of a plurality of thresholds of cumulative aerosol volume generated during the usage session. The thermal profile is preferably stored inside the memory module 28 of the aerosol-generating device 10. When a user applies each puff of a series of puffs to the device 10, a volume of aerosol is generated and the cumulative volume of aerosol is determined, for example by calculation or flow measurement. The control electronics 27 access the memory 28 read the thermal profile and the control electronics 27 then control the supply of power from the battery 26 to the heater 40 to adjust the target operating temperature for the heater in accordance with the thermal profile of FIG. 5 and the cumulative volume of aerosol generated during the usage session. Thus, taking the thermal profile of FIG. 5 as an example, the usage session may have a maximum threshold of aerosol volume of 660 ml. Once 660 ml of aerosol has been generated the usage session is ended. The usage session may be split into a plurality of phases, each phase ending when a threshold has been reached in the cumulative volume of aerosol generated during the usage session. As an example, the usage session may be split into 12 phases, each of the 12 phases ending after a threshold volume of 55 ml of aerosol has been generated. The first phase may, thus, end after generation of a first threshold of 55 ml of cumulative volume of aerosol has been generated, a second phase may end after a second threshold of 110 ml cumulative volume of aerosol has been generated, a third phase may end after a third threshold of 165 ml cumulative volume of aerosol has been generated, and so on until the end of the usage session. In the exemplary thermal profile illustrated in FIG. 5 , the temperature of a heater is initially raised to a target operating temperature of 350° C. After generation of a cumulative volume of 55 ml of aerosol the target operating temperature is reduced to 320° C. After generation of a cumulative volume of 275 ml of aerosol, the target operating temperature is increased to 326° C. After generation of a cumulative volume of 385 ml of aerosol, the target operating temperature is increased to 332° C. After generation of a cumulative volume of 440 ml of aerosol, the target operating temperature is increased to 338° C. After generation of a cumulative volume of 495 ml of aerosol, the target operating temperature is increased to 344° C. After generation of a cumulative volume of 550 ml of aerosol, the target operating temperature is increased to 350° C. The operating temperature remains at 350° C. until the usage session is ended.

The volume of aerosol generated, and the cumulative volume of aerosol generated over the duration of the usage session, may be determined by measurement of airflow through the device. For example, an airflow sensor, or airflow sensing means, may provide a volume for airflow from which volume of aerosol generated may be calculated. Conveniently, the volume of aerosol generated, and the cumulative volume of aerosol generated, may be determined by monitoring a signal representative of power supplied to the heater, determining user puffs by interpreting variations of the signal representative of power supplied to the heater, and calculating a volume of aerosol associated with each user puff. An advantageous method of determining volume of aerosol generated may be as follows.

An overview of an exemplary method is schematically illustrated in FIG. 6 . A user inserts an aerosol-generating article into the aerosol-generating device and initiates a usage session by actuating the user button 50. This indicates the start of the user experience 601. Power is supplied from a battery in the aerosol-generating device to the heater element 40 until the heater element reaches an initial operating temperature. This temperature may be, for example, about 330° C. in accordance with the temperature profile of FIG. 5 .

The power signal of the power supplied to the heater is monitored 602. The user then takes a puff 603. When the user puffs, the heater is cooled because of the airflow. Thus, the power that needs to be supplied to the heater to maintain the operating temperature increases. The power supplied increases and the correct temperature is maintained.

The presence of a user puff is detected by analysing the power signal 604. A puff start point and a puff end point are determined by means of this analysis.

The energy of the detected puff is then calculated 605 and the volume of aerosol generated during the puff is also calculated 606. Volume generated during each puff is added to provide a cumulative total of volume generated during the usage session 607.

In a query step 608, if the cumulative total volume equals or exceeds the predetermined maximum permissible aerosol volume for the usage session (for example 660 ml) the usage session is ended 609.

If the cumulative total volume does not equal or exceed the predetermined maximum permissible aerosol volume for the usage session then, in a further query step 610, the controller determines whether the cumulative total volume equals or exceeds an intermediate threshold set for changing the operating temperature of the heater. If not, the process reverts to step 602. The session remains active and the user may take another puff.

If the cumulative total volume does equal or exceed such an intermediate threshold (for example the 275 ml threshold indicated in FIG. 5 ) the operating temperature of the heater is altered (for example increased to 326° C. as indicated by FIG. 5 ) and the process reverts to step 602. The session remains active and the user may take another puff, but the operating temperature has been changed.

The usage session remains active until the user has generated the maximum permissible aerosol volume or until a maximum time threshold is reached. During the usage session, the operating temperature of the heater is varied as different intermediate thresholds of cumulative aerosol volume are met, for example as described above in relation to FIG. 5 .

Many factors affect a power signal under operating conditions and power as a function of time in an aerosol-generating device is noisy and complicated. In real applications a power signal carries background noise and it is not simple to associate with certainty a specific behaviour to the occurrence of a puff. Simple threshold analysis of the power signal to determine puffs may only allow an approximate quantification of the volume of aerosol generated. While an approximate quantification may allow control of temperature as a function of generated aerosol volume with significant benefits to a user experience, it may be desirable in some circumstances to provide a more accurate quantification of the volume or aerosol generated.

In order to provide a more accurate determination of puff start points and puff end points, and therefore a more accurate quantification of cumulative aerosol volume, two moving averages of power as a function of time may be compared. Relationships between the two moving averages may be analysed in real time and specific points, including a puff start point and a puff end point, may be determined. Specific points determined by the analysis of the two moving averages may be termed trigger points.

FIG. 7 shows a graph illustrating power supplied to a heater as a function of time. The function P (power) of time has the trend depicted in the graph as a square curve 501.

A first moving average 502 (MA1) is an average value of the power signal over a first time window TW1. The first time window TW1 is, in this specific example, approximately 400 ms. A second moving average 504 (MA2) is an average value of the power signal over a second time window TW2. The second time window TW2 is, in this specific example, approximately 1000 ms.

In a first portion of the graph 503, the heater is at a constant temperature and the user is not taking a puff. Thus, power supplied to the heater to maintain the operating temperature is constant and equal to a value shown as A on the graph. In the first portion of the graph 503 the value of the first moving average 502 coincides with the value of the power 501, as the power is constant and equal to a value A, therefore the average value over time window TW1 is also constant over time. In the first portion of the graph 503 the value of the second moving average 504 coincides with the value of the power 501, as the power is constant and equal to a value A, therefore the average value over time window TW2 is also constant over time.

When a user takes a puff, the heater is cooled by the resulting airflow. Thus, the power supplied to the heater needs to increase to maintain the heater at its operating temperature. As depicted in FIG. 7 , the power increases from the value denoted as A to a higher value denoted as B. As the user completes a puff, the power needed to be supplied to the heater to maintain an operating temperature decreases, and the power supplied decreases back to the maintenance level denoted by A.

After the increase in power, the first moving average progressively increases, but not as steeply as the power signal since it also includes a portion of signal which is still at value A. The first moving average continues to increase until there is coincidence with the power value. Then it decreases in similar fashion after the power decreases again.

After the increase in power, the second moving average progressively increases. As the second moving average is based on a longer time window TW2 than the first moving average, the second moving average starts to rise in the proximity of the puff region but more gradually than the first moving average.

Having obtained a first moving average and a second moving average, conditions may be set in order to detect a puff. Firstly, a significant event is defined, identified as the moving average cross-over: MA1=MA2+δ1. When the first moving average equals the second moving average plus a first constant (δ1), the event is called moving average cross-over. The constant δ1 is a value experimentally determined. According to a preferred specific example, the first constant (δ1)=0.22 W. A puff start is determined to have occurred when the relationship between the first moving average and the second moving average meets, or exceeds, the conditions defined for the moving average crossover. That is, a puff start is determined to have occurred when the relationship between the first moving average and the second moving average changes from MA1<MA2+δ1 to MA1=MA2+δ1 or MA1>MA2+δ1. The moving average cross-over corresponds to a perturbation of the power signal that is big enough to be quantified as a puff. This methodology has an advantage when the power signal carries a lot of background noise, and the behaviour correspondent to the occurrence of a puff otherwise may not be easy to detect.

Conditions may also be defined which, when verified, are indicative of the occurrence of a puff. After the moving average crossover has been detected, then four conditions (or triggers) may be verified to spot a puff by monitoring the power signal. These validation conditions, or triggers, can be identified as Trigger 1, Trigger 2, Trigger 3, and Trigger 4, and are defined as follows.

TRIGGER 1: The condition for trigger 1 is MA1>MA2+δ1. Trigger 1 is tied to the puff start. When trigger 1 is detected, immediately after the moving average cross-over, then the system knows that such detection corresponds to the beginning of a puff.

TRIGGER 2: The condition for trigger 2 is MA2>MA1+δ2. Trigger 2 identifies the peak of the puff. In this case, δ2 is a second constant. According to the preferred specific example, the second constant (δ2)=0 W. The position of Trigger 2 is illustrated in FIG. 8 .

TRIGGER 3: The condition for trigger 3 is MA2>MA1+δ3. This trigger identifies the fading of the puff, δ3 is a third constant.

TRIGGER 4: The condition for trigger 4 is MA1>MA2−δ41 AND MA2<MA2 1ST+δ42.

This trigger detects the end of the puff, δ41 is a fourth constant and δ42 is a fifth constant. δ41 and δ42 are experimentally calculated. According to the preferred specific example the fourth constant δ41 is 0.06 W and the fifth constant δ42 is 0.31 W. The conditions for trigger 4 are illustrated in FIG. 9 .

FIG. 10 illustrates detection of a puff in a further specific example. For this specific embodiment, the first moving average (MA1) was based on a time window of 128 ms and the second moving average (MA2) was based on a time window of 512 ms.

A puff is detected when the moving average cross over occurs 801. This is the point when MA1=MA2+δ1. δ1 is a constant that is experimentally determined and has a value of 0.22 W. The first trigger occurs when MA1>MA2+δ1, i.e. immediately after the puff start.

The second trigger 802 occurs when MA2>MA1+δ2. δ2 is a constant that is experimentally determined and has a value of 0 W. Thus, the second trigger occurs when MA2>MA1

The third trigger 803 occurs when MA2>MA1+δ3. δ3 is a constant that is experimentally determined and has a value of 0.18 W.

The fourth trigger 804 occurs when MA1>MA2−δ41 AND MA2<MA2 1ST+δ42. δ41 is a constant that is experimentally determined and has a value of 0.06 W. δ42 is a constant that is experimentally determined and has a value of 0.31 W. The puff is deemed to end at the fourth trigger.

In order to improve the accuracy of the puff detection, a set of time thresholds may be established between different triggers. Such thresholds facilitate valid detection of puffs in very different volumes and flows. Time thresholds, or timeouts, are durations that initiated after a trigger is activated. If the following trigger is not activated after a predetermined period of time, the detection process is reset. This allows to discard “badly detected” triggers.

A first timeout may be initiated after the first trigger. If the second trigger is not detected within a predetermined period of time the puff detection is rejected and the detection system is reset. In a specific example the first timeout may have a duration of 2.5 seconds. Thus, if the second trigger is not detected within 2.5 seconds of the first trigger, the detection of the puff is rejected.

A second timeout may be initiated after the third trigger. If the fourth trigger is not detected within a predetermined period of time the puff detection is rejected and the detection system is reset. In a specific example the second timeout may have a duration of 3.5 seconds. Thus, if the fourth trigger is not detected within 3.5 seconds of the third trigger, the detection of the puff is rejected.

After the end point of the puff has been identified (fourth trigger), the volume of the puff is calculated from the integral of power in time from the puff start to the puff end. The integral of the power over time equals the energy. The energy in turn corresponds to the heat injected into the consumable, and the heat is what the user takes away with a volume of cooling airflow.

As illustrated in FIG. 11 , it will be appreciated that the energy strictly associated to a puff may be calculated as the integral calculus of the power signal during the puff, minus the energy that would be spent anyway even without a puff, as indicated in the formula:

The energy is correlated to the volume through a relationship that has been determined empirically. Similarly, it is also possible to correlate the power to the air flow, which equals the volume per time unit.

The usage session, which may be termed a user experience, has a maximum permissible cumulative volume of aerosol to be delivered. Every puff contributes to the cumulative volume. As the cumulative volume reaches various predetermined thresholds during the usage session, the operating temperature of the heating element may be varied to optimise the generation of aerosol from the aerosol-forming substrate.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number “A” may be understood as “A”±10% of “A”. Within this context, a number “A” may be considered to include numerical values that are within general standard error for the measurement of the property that the number “A” modifies. The number “A”, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which “A” deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. 

1.-15. (canceled)
 16. A method of operating an aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising a power supply configured to supply power to a heating element to heat the aerosol-forming substrate, and a controller, the method comprising steps of: monitoring a user interaction parameter indicative of use of the aerosol-generating device during the usage session; using the user interaction parameter as a parameter for controlling temperature of the heating element during the usage session; monitoring a parameter indicative of aerosol generation during the usage session; analyzing the monitored parameter indicative of aerosol generation to identify a user puff, the user puff defined by a puff start and a puff end; analyzing the monitored parameter indicative of aerosol generation during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff; and using the puff volume as the user interaction parameter for controlling temperature of the heater element.
 17. The method according to claim 16, wherein a value of the user interaction parameter is associated with a target operating temperature of the heating element, and wherein a cumulative value of the user interaction parameter recorded during the usage session is associated with a target operating temperature of the heating element.
 18. The method according to claim 16, wherein the aerosol-generating device stores a predetermined thermal profile defining a heating element temperature with respect to a value of the monitored user interaction parameter.
 19. The method according to claim 18, wherein the value of the monitored user interaction parameter is a cumulative value of the user interaction parameter during the usage session.
 20. The method according to claim 18, wherein the operating temperature of the heating element during the usage session is controlled in accordance with the predetermined thermal profile.
 21. The method according to claim 16, wherein the user interaction parameter is indicative of volume of aerosol released by the aerosol-forming substrate during the usage session.
 22. The method according to claim 16, further comprising the step of analyzing the monitored parameter indicative of aerosol generation to identify a plurality of user puffs performed during the usage session, each of the plurality of user puffs having a puff start and a puff end determined by analyzing the monitored parameter indicative of aerosol generation.
 23. The method according to claim 22, further comprising the steps of: analyzing the monitored parameter indicative of aerosol generation during each of the plurality of identified user puffs to calculate a puff volume for each of the plurality of user puffs; determining a cumulative puff volume of aerosol generated during each of the plurality of identified user puffs; and using the cumulative puff volume as the user interaction parameter for controlling temperature of the heater element.
 24. The method according to claim 16, wherein the step of analyzing the monitored parameter indicative of aerosol generation comprises steps of calculating a first characteristic of the monitored parameter indicative of aerosol generation and analyzing the first characteristic to determine a puff start and a puff stop.
 25. The method according to claim 24, wherein the step of analyzing the monitored parameter indicative of aerosol generation further comprises steps of calculating a second characteristic of the monitored parameter indicative of aerosol generation and analyzing both the first characteristic and the second characteristic to determine the puff start and the puff stop.
 26. The method according to claim 24, wherein the first characteristic is a first moving average value of the monitored parameter computed on a first time window having a first time window duration.
 27. The method according to claim 24, wherein the first characteristic is a first moving median value of the monitored parameter indicative of aerosol generation computed on a first time window having a first time window duration.
 28. An aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply configured to supply power to generate the aerosol; and a controller configured to monitor a user interaction parameter indicative of use of the aerosol-generating device during the usage session, and to use the user interaction parameter to control the temperature of the heating element during the usage session, wherein the aerosol-generating device is configured to monitor a parameter indicative of aerosol generation during operation of the aerosol-generating device, analyze the monitored parameter to identify a user puff, the user puff defined by a puff start and a puff end, analyze the monitored parameter during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff, and control the temperature of the heating element based on the calculated puff volume.
 29. The aerosol-generating device according to claim 28, wherein the aerosol-generating device is further configured to: monitor a user interaction parameter indicative of use of the aerosol-generating device during the usage session, use the user interaction parameter as a parameter for controlling temperature of the heating element during the usage session, monitor a parameter indicative of aerosol generation during the usage session, analyze the monitored parameter indicative of aerosol generation to identify a user puff, the user puff defined by a puff start and a puff end, analyze the monitored parameter indicative of aerosol generation during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff, and use the puff volume as the user interaction parameter for controlling temperature of the heater element.
 30. An aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply configured to supply power to generate the aerosol; a controller; and a nontransitory computer-readable medium containing instructions to carry out a method of monitoring a user interaction parameter indicative of use of the aerosol-generating device during the usage session, and using the user interaction parameter as a parameter for controlling temperature of the heating element during the usage session, wherein the aerosol-generating device is configured to monitor a parameter indicative of aerosol generation during operation of the aerosol-generating device, analyze the monitored parameter to identify a user puff, the user puff defined by a puff start and a puff end, analyze the monitored parameter during the user puff to calculate a puff volume, the puff volume being a volume of aerosol generated during the user puff, and control the temperature of the heating element based on the calculated puff volume.
 31. An aerosol-generating device for generating an aerosol from an aerosol-forming substrate during a usage session, the aerosol-generating device comprising: a power supply configured to supply power to generate the aerosol; a controller; and a nontransitory computer-readable medium containing instructions to carry out a method according to claim
 16. 